The present invention relates to an electrostatic microactuator, a method of activating the same, and a camera module used with the same, and more particularly, it relates to an electrostatic microactuator electrostatically powered, assembled easily, and having improved smoothness, stability, and reliability in actuation, a method of activating such an electrostatic microactuator, and a camera module used with the same.
For recent years, a miniaturized linear actuator of more downsized design, precise operation and reduced cost has been increasingly needed for focal adjustment of a super-compact camera, for example. An example of a solution to such needs is an electrostatic actuator disclosed in Japanese Patent Laid-Open Publication H08-140367.
FIG. 27 is a schematic diagram showing a structure of the prior art electrostatic actuator.
As shown in FIG. 27, an electrostatic actuator 101 is comprised of a movable piece 102 and a couple of statical members 103a and 103b overlaid on the opposite sides of the movable piece. The statical members 103a and 103b have their respective two groups of branch pads connected to electrodes, and there are four groups of branch pads connected to electrodes A to D for the couple of the upper and lower statical members.
Branch pads in the statical members 103a and 103b, which are connected to corresponding ones of the electrodes A to D, are arranged at the same pitch with branch pads 104 of the movable piece 102, and all the branch pads are the same in width in both the statical and movable pieces. In the static pieces 103a and 103, however, the branch pads separately correlated with two of the electrodes (e.g., electrodes A and C) are alternately placed in an interlacing deployment. In addition to that, the branch pads of the upper and lower static pieces 103a and 103b are correlated with one another in a ½ out-of-phase pattern where the upper branch pads are deviated by a half of their respective width from their counterparts or the lower branch pads.
Applying high voltage to the electrode A, an electrostatic force (Coulomb force) developed between the electrode A and the branch pads 104 correlated with an electrode E causes the movable piece to be attracted by the upper statical member 103a (toward a position where the branch pads correlated with the electrodes A and E are aligned in phase). Then, switching the electrode supplied with the high voltage to the electrode B, the movable piece 102 is attracted by the lower statical member 103b (toward a position where the branch pads correlated with the electrodes B and E are aligned in phase). In this way, the succeeding switching of the electrodes as in a manner of A to B, B to C, C to D, and so forth enables the movable piece 102 to microscopically vertically vibrate and macroscopically laterally move (e.g., move to the right in FIG. 27 with one degree of freedom).
Supplying the high voltage to the electrodes in the reversed order as in A to D, D to C, C to B, and so forth enables the movable piece to move to the left in FIG. 27.
To implement such a way of the motion, the vertically juxtaposed statical members 103a and 103b must be under accurate control of the phases or the branched-electrode pattern, and the movable piece 102 must also have an accurately fabricated electrode pattern on both the opposite sides. This requires time consuming and complicated assembling task and accordingly leads to a cost increase, which are some of problems that must be overcome for a mass-production of such a high precision actuator.
Further, since the movable pieces in this electrostatic actuator vibrates with a relatively large amplitude between the juxtaposed statical members 103a and 103b to laterally move pitch by pitch, its microscopic movement is not satisfactorily smooth, and it is desirable to improve both the physical and operational mechanisms of the actuator.